Arc welders of the type that utilise a stick, often referred to as slick welders, have a lethal voltage present at the welding stick, when activated. While this voltage may fall to about 12V to 20V when welding operations are under way, the voltage can rise to up to 100V under open-circuit conditions. While 12 to 20V is not likely to be fatal, in the unlikely chance of a person coming into contact with the stick during welding, 100V can be fatal if a person comes into contact with it. In any event, the chance of a person coming into contact with the open circuit stick carrying up to 100V is greater than the chance of coming into contact with the stick during a welding operation.
Arc welders of the type described above are controlled by a switch (sometimes contained in the handset), which causes a control circuit to operate. In a DC arc welder, the control circuit controls generation of the DC current which is delivered to the welding rod or welding stick, which is held in the handset, the handset being moveable to allow the person welding to manipulate the welding stick over the work as the welding operation progresses. When the switch is operated, the control circuit causes a direct current (DC) voltage to be switched to the stick. Under open circuit conditions which are present before welding commences the voltage rises to up to 100 VDC. It is at this time that a person coming into contact with the stick is at risk of electric shock or electrocution.
It is an object of the present invention to provide a safety interlock in an arc welder to minimise the risk of electric shock or electrocution.
Some types of arc welder utilise AC power to preform welding operations. While part of the aforementioned discussion is made with reference to DC arc welders, it should be understood that the invention to be described has equal application in AC arc welders.
Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.